AbstractThe Calabrian Arc is a narrow subduction-rollback system resulting from Africa/Eurasia plate convergence. We analysed the structural style of the frontal accretionary wedge through a multi-scale geophysical approach. Pre-stack depth-migrated crustal-scale seismic profiles unravelled the overall geometry of the subduction complex; high-resolution multi-channel seismic and sub-bottom CHIRP profiles, together with morpho-structural maps, integrated deep data and constrained the fine structure of the frontal accretionary wedge, as well as deformation processes along the outer deformation front.

We identified four main morpho-structural domains in the western lobe of the frontal wedge: the proto-deformation area at the transition with the abyssal plain; two regions of gentle and tight folding; a hummocky morphology domain with deep depressions and intervening structural highs; a highstanding plateau at the landward limit of the salt-bearing accretionary wedge, where the detachment cuts through deeper levels down to the basement. Variation of structural style and seafloor morphology in these domains are related to a progressively more intense deformation towards the inner wedge, while abrupt changes are linked to inherited structures in the lower African plate. Our data suggest focusing of intense shallow deformation in correspondence of deeply rooted faults and basement highs of the incoming plate.

Back-arc extension in the Southern Tyrrhenian Sea has recently ceased, producing a slowdown of slab rollback and plate-boundary re-organization along trans-tensional lithospheric faults segmenting the continental margin. In this complex setting, it is not clear if the accretionary wedge is still growing through frontal accretion. Our data suggest that shortening is still active at the toe of the wedge, and uplift rates along single folds are in the range of 0.25-1.5 mm/yr. An unconformity within the Plio-Quaternary sediments suggests a discontinuity in sedimentation and tectonic processes, i.e. a slowdown of shortening rate or an increase in sedimentation rate, but not a real inactivation of frontal accretion, which still contributes to the migration of the outer deformation front towards the foreland.

AbstractThis study addresses selected aspects of the stratigraphic-structural setting of the outermost Calabrian Arc accretionary wedge and underlines relationships between structural development and Messinian evaporite stratigraphy through the analysis of re-processed CROP multichannel seismic reflection profiles.
A detailed seismostratigraphic analysis, calibrated with P-velocities compiled by previous works, images a general bipartition of the Messinian evaporite deposits: the transparent «lower subunit» appears to have undergone ductile-flow deformation», with the development of salt-cored thrusting structures, and the layered «upper subunit» appears to be characterized by brittle deformation.
The difference in both the seismic facies and the deformational style imaged for the Messinian evaporite unit allows a better defined unit stratigraphy that consists of a salt layer below and a gypsum and marl layer above.
Lateral variations in composition and/or thickness of the Messinian evaporites are the local cause of the replacement of the transparent and layered subunits with a more chaotic facies as well as a change in the deformation style, with the development of doubleverging imbricated thrust sheets of the whole Messinian sequence.
Most of the accreted outermost accretionary wedge is imaged to have resulted from the progressive piling up and associated thrusting of the Messinian evaporites and overlying Plio-Quaternary sediments; the gently dipping-reflector located at the base of the Messinian evaporites shows negative polarity at some places, suggesting that it acts as the décollement level.
Active deformation occurs on the outermost accretionary wedge as related to subduction-driven shortening; further on, near-surface gravitational slide tectonics is imaged as related to a growing outermost wedge and favoured by the salt tectonics and/or to fluid overpressuring on the décollement level.